If primary invitees who are invited to join an instant message collaboration are unavailable, it is desirable to invite backup invitees. In conventional instant messaging systems, such as the system disclosed in U.S. Patent Application Pub. No. US 2004/0205134, determining the unavailability of a primary invitee and then inviting a backup invitee are based on limited, inflexible and incomplete conditions and attributes of the invitees and of the collaboration. The known instant messaging systems make invitee unavailability and backup invitee decisions based on information such as the invitee's online presence, availability filtering, who initiated the collaboration, the collaboration's topic, and whether an invitee is defined as a necessary attendee. Reliance on such limited information fails to detect other indications of an invitee's unavailability to participate in the collaboration and the related need to invite a backup invitee. Thus, there exists a need to overcome at least one of the preceding deficiencies and limitations of the related art.